Even jacks regular part A is too non uniform like that, to mix small quantities anyway, IMO. It was made for mixing stock solutions on a way bigger scale than most hobby growers would. Commercial farmers likely crack open whole bags at a time, and use up large portions of it if not dump the whole thing in.. Like it was intended to be.
When your pulling out a little scoop that's only a few grams or more at a time, there is no way your getting the proper ratios, as you can literally see there is more of one component than the others. Just like pouring a few M&M candies out the bag, you only get a few of the same color sometimes.. however if you dump the half the bag or more in your hand and you would expect to get all the colors. lol I dunno....
When you mix up a stock batch it's way closer to being uniformly balanced overall, simply for the fact your mixing in way bigger scoops, which are sure to be blended up with the proper ratios, and not missing or in excess of some of the elements. Not to mention, its so much easier to use that way, without mixing and dealing with it dry each time. I just measure by EC and add it up for each part as I go when mixing up a res, until I'm confident enough I know the exact volume of the liquid needed each time coming from that particular batch. Then treat it like any other liquid 2 part bottled nutes, adding so many mils at a time from each bottle. Double checking once in awhile. I've heard its ok to mix the mag sulfate right in with part A in the same super concentrated stock solution, but haven't tried that yet. Even easier!
I'm still waiting for someone to comment on the new non N formula before I pick up a bag. I already know Jacks is probably perfect now with that option. Despite the excess nitrogen in the regular part A, I'm still happy with the outcome, but the plants sometimes exhibit some minor flaws due to it, depending on the setup\medium.. I bet with the zero N it will be perfect dialed in grows every time, with more flexibility like the other 3 part solutions give.. Its good enough now ( especially DWC, with hardly any salt buildup) I'm reluctant to even change anything..